The disclosure herein relates to devices and/or methods for treating conditions, such as heart failure, hypertension, etc., using breathing therapy.
Heart failure typically refers to the inability of the heart to keep up with the functional demands made upon it. Congestive heart failure typically refers to an inability of the heart to pump an adequate amount of blood to the body tissues. In other words, congestive heart failure is characterized by inadequate cardiac output.
Because the heart is unable to pump an adequate amount of blood, blood returning to the heart becomes congested in the venous and pulmonary system. A patient with congestive heart failure may be unable to pump enough blood forward to provide an adequate flow of blood to the kidneys, for example, causing the patient to retain excess water and salt. The patient's heart may also be unable to handle the blood returning from the patient's pulmonary system, resulting in a damming of the blood in the lungs and increasing the risk of developing pulmonary edema.
Symptoms experienced by a patient with congestive heart failure may include breathing difficulty caused by pulmonary edema, swelling, particularly of the lower extremities, fatigue, difficulty concentrating, dizziness, and fainting. During periods where a patient with congestive heart failure is experiencing severe symptoms, breathing difficulty may be such that the patient cannot lie down to sleep, and the patient may feel as though they are suffocating.
Patients with congestive heart failure may be treated with pharmacological therapies to increase cardiac output. Some patients with congestive heart failure benefit from an implanted pacemaker that increases cardiac output by increasing the heart rate, or synchronizing the contraction of the ventricles of such patients. When a patient experiences severe symptoms, the patient may be admitted to a hospital or clinic, and receive supplemental pharmacological therapy to alleviate the symptoms. This situation may be very costly because of the hospital stay, nursing costs, patient transportation costs, and so forth.
Generally, chronic heart failure (HF) is accompanied by a sustained elevation in sympathetic nervous system activity (e.g., a sustained elevation of sympathetic tone) which is thought to be an important component in the pathophysiology and progression of the disease. Hypertension or elevated blood pressure is generally indicative of an elevated sympathetic tone. Further, HF patients may also show abnormal breathing patterns with an increased respiratory rate and a lower tidal volume. Faster respiratory rate is associated with higher levels of sympathetic activity and has a negative impact on the functioning of the heart. All these factors contribute to the distressing symptoms of fatigue, dyspnea and exercise intolerance in these patients.
It has been shown that when a slow breathing technique was taught to patients with heart failure (e.g., employing a scripted technique that directed patients to modify their breathing rate), they had a reduction in their sensation of shortness of breath and an improvement in their exercise performance (see, Swanson et al., “The effect of biofeedback on function in patients with heart failure” Appl Psychophysiol Biofeedback, 2009; 34(2):71-91). Further, studies have shown that slow breathing, when directed and performed routinely, can lower blood pressure (see Elliot et al., “Graded blood pressure reduction in hypertensive outpatients associated with use of a device to assist with slow breathing,” J Clin Hypertens, 2004; 6(10):553-9; and Viskoper et al., “Nonpharmacologic Treatment of Resistant Hypertensives By Device-Guided Slow Breathing Exercises,” AJH, 2003; 16:484-487.
Further, U.S. Pat. App. Pub. No. US2007/0118183 to Gelfand et al., published May 24, 2007, and entitled “System and Method to Modulate Phrenic Nerve to Prevent Sleep Apnea,” describes a device for treating breathing disorders such as central sleep apnea using stimulation provided to the phrenic nerve through a transvenous lead system. Unlike other breathing modification devices, such as “Breathing Pacemakers” of Avery Biomedical Devices, Inc. that stimulate the phrenic nerves to cause diaphragm contraction, U.S. Pat. App. Pub. No. US2007/0118183 describes use of stimulation beginning after inspiration to extend the duration of a breath and to hold the diaphragm in a contracted condition (e.g., prolong diaphragm contraction).